This invention relates generally to a device for use in a draw tube of a lathe for accommodating workstock having diameters less than the internal dimension of the lathe's draw tube.
Lathes used in industrial machine shops typically include what is known as a draw tube or "draw bar". Through this draw tube, which is generally cylindrical, the raw stock to be worked is inserted in a free end of the draw tube. The other end of the draw tube terminates within the lathe adjacent a chuck, which clamps against the raw stock to support the stock as the stock is rotated in the lathe. As the stock is rotated in the lathe, cutting implements, shaping implements, and other tool members are used to provide the desired profile in the stock and for cutting the stock.
Because lathes generally rotate the stock at a relatively high rate of speed, some times approaching several thousand revolutions per minute ("RPM"), it is essential that the stock be securely constrained throughout its length, both for maintaining control of the stock during lathe operations, and also for safety reasons. This stock restraint requirement generally requires the interior diameter of the draw tube to approximate the exterior diameter of the stock being worked. Otherwise, the stock will tend to not only be rotated with the lathe, but can also tend to revolve, or in some cases "orbit" about the free end of the draw tube. This can produce severe production and safety problems.
In order to prevent this from happening, draw tubes having inner diameters substantially matching the raw stock to be worked are available as inserts for the draw tube. Typically, these draw tube inserts provide for an inner diameter which is less than the standard draw tube found on the machine, for allowing smaller diameter stock to be worked. However, such draw tube inserts can be cost-prohibitive when a large variety of smaller diameters of stock are used, because a separate draw tube insert may be required for each smaller diameter stock. Further problems with such an arrangement include the storage requirements for such a large number of inserts and the fact that each insert must be custom-made using special production facilities, which may not allow an insert of a particular inner diameter to be readily produced in a conventional machine shop.
While the foregoing inserts are known, there still exists a need for an economical adaptor usable with a variety of workstock diameters.